As intracellular pathogens, tubercle bacilli possess the capacity to replicate within the phagocytic cells whose tasks include immune induction and bacterial killing. Successful intracellular infection depends on thwarting these functions. Monocytes from patients with pulmonary tuberculosis indeed function abnormally, inhibiting T cell responses to mycobacterial antigens because of direct activation by mycobacterial products. Using 2-D gel electrophoresis and the technique of monocyte western blotting, a novel 58 kD protein of virulent M. tuberculosis has been demonstrated in this laboratory with the unique capacity to induce cytokine production in human monocytes. Given the intimate and complex relationship between M. tuberculosis and its cellular host, it is likely that this protein is involved in mechanisms affecting both intracellular parasitism and regulation of host immunity. The specific aims of this application therefore will be: l) the purification of the 58, 20 and 44 kD monocyte activating proteins, determining their cellular localization and investigation of possible precursor/product interrelationships; 2) the cloning, sequence analysis and epitope mapping of the 58 kD protein; 3) investigation of the mechanism for triggering of host cell responses to the 58 kD protein, including the role of serum binding proteins, identification of the cell surface receptor, and investigation of the pathway(s) involved with signal transduction; and 4) analysis of cellular responses to the 58 kD protein, including phagocytosis, killing, nitric oxide and superoxide production, and cytokine expression. This is a health related project.